The present invention relates to a copier having an editing function and operable in a trimming mode for extracting part of an image printed on a document as a trimmed image and transferring it to a paper sheet, a masking mode for omitting part of the image as a masked image and transferring a non-masked image surrounding the masked image to the paper sheet, and a centering mode combinable with either one of the trimming mode and masking mode for shifting the center of the image on the document into register with the center of the paper sheet and transferring it to the paper sheet.
Most of copiers with an editing function do not allow one to select a centering mode in combination with either one of the trimming mode and masking mode, because the resulting combined mode would be complicated. Nevertheless, there has been proposed a copier with an editing function which is capable of meeting the user's need for the combined trimming mode or masking mode and centering mode. This type of copier is usually constructed such that when centering accompanies the trimming mode or the masking mode, marked part of a document image, i.e., a trimmed image or a masked image is located at the center of a paper sheet with the trimmed image or the masked image itself being used as a reference. More specifically, centering is executed such that the center of the trimmed image or that of the masked image itself coincides with the center of a paper sheet. Locating the center of the trimmed image at the center of a paper sheet does not matter at all because the trimmed image is the image to be transferred. Regarding the masked image, however, it is not the image to be transferred to a paper sheet, i.e., a non-masked image surrounding the masked image is the desired part of the document image. Furthermore, the masked image is not always located at the center of the non-masked image. For example, assume that the masked image is noticeably deviated from the center of the non-masked image, and that the non-masked image has a substantial size. Then, when the center of the masked image is brought into register with the center of a paper sheet, it is likely that the image to be transferred is partly located outside of the range of the paper sheet and thereby partly lost, depending on the size of the paper sheet.